Venous leg ulcers affect between 1% and 1.5% of the UK population at any given time. Based on 60 million persons, this equates to approximately 200,000 with ulcers requiring treatment. Estimates of cost to treat range from £450 million to £800 million per year. In the USA, the estimate of cost to treat comes in at almost $5 billion per year. The average length of time any one person has an ulcer for is upwards of two years. If an ulcer does heal, relapse rates are as high as 50% at six months, without precautionary measures.
A mainstay of treatment is multi-layered graduated compression bandaging; using an elasticated bandage, higher pressure is exerted at the ankle, the bandage becoming progressively less compressive up to the knee. Bandaging up beyond the knee is not necessary. The application of excessive pressure can cause discomfort or harm to a patient. The application of insufficient pressure has negative consequences on the healing process, and may also provide insufficient support or fail to maintain the bandage in place. Accordingly, there is a need to apply correct graduated compression. This is a highly skilled task, e.g. requiring nurses to undertake training courses. Health care practitioners generally become competent only through years of experience.
Many compression bandage types exist on the market, all with different stretch characteristics, and many techniques for application exist. These factors make it exceptionally difficult to get the graduated compression profile absolutely correct, so as to maximise the chance that the ulcer eventually heals.
Individual diaphragm pressure sensors are well known and can be air-filled, water-filled, oil-filled, etc. Commercially available rigs for noting the compression ability of graduated compression socks on, for example, a test mannequin are based on a diaphragm system. However, the problem of ensuring correct usage remains.
WO2006/013422 reviews known pressure sensors, and proposes a sensor that may be placed directly on the body or between the windings of a bandage. Such a pressure sensor, for providing an indication of the pressure applied by a bandage to a human or animal body, comprises an elongate, flexible support strip adapted to be placed between a bandage and the body, the strip carrying a flat pressure-sensitive portion whose electrical properties vary with applied pressure normal to the plane of the strip, and also carrying flat, flexible conductors for connecting the pressure-sensitive portion to a supply of electricity and to means for providing an indication of the applied pressure. The pressure-sensitive portion is a Quantum Tunnelling Composite (QTC), a material available in flexible form as sheets and whose conductivity changes in accordance with pressure applied across the plane of the sheet.
The use of a flat pressure-sensitive portion allows the provision of a thin strip that can be readily introduced underneath or between the windings of a bandage, and can also be removed after use. The device is however dependent on the use of a QTC material, and has disadvantages including (i) the difficulty of producing a homogeneous composite material such that the electrical response is uniform throughout the device, and (ii) the fact that the magnitude of the obtained signal from such a sensor may be low and also compromised by the level of noise, and (iii) the likelihood that incorrect measurement will be recorded if the bandage is pulled laterally across the device. In addition, if a raised area is used to obtain good results, it may be difficult to remove the device from a bandage. Furthermore, the device may be uneconomical as a single-use, disposable product.